Reactor system with several reactor units in parallel

ABSTRACT

The invention concerns a reactor system suitable for carrying out chemical reactions, having one or more common reactant feed lines, two or more single unit operated reactor sections and one or more common product discharge lines. The reactor system is especially suitable for the production of hydrocarbons from synthesis gas over a catalyst.

The present invention relates to a reactor system suitable for carryingout chemical reactions, the system comprising two or more single unitoperated reactor sections. More specifically, the invention concerns thecatalytic conversion of synthesis gas into long chain hydrocarbons in areactor system comprising a multitude of multitubular fixed bed reactorssections.

Much attention has been given in the past and is still given at thepresent moment to the scale-up of chemical processes, which in mostcases results in the scale-up of chemical reactors. Usually it is moreefficient (economical) to use one large scale reactor than a multitudeof independently operated smaller reactors.

An important requirement in the scale-up of reactors, especiallychemical reactors, is that a large, commercial reactor should operate ina predictable fashion, which could be a factor of 10,000 larger or evenmore than laboratory and development reactors. It is important that thereactor operates within a safe set of conditions with a predictableoutput and quality at a predictable cost. Changing the scale of areaction alters the heat removal and mixing characteristics of thereaction zone, which may result in differences in temperature andconcentration profiles. This may than result in amended chemistry, thusinfluencing productivity, selectivity, catalyst deactivation etc. of thereactor. This means that the performance of a large reactor is difficultto predict on the basis of the performance a small reactor. Thus,extensive scale-up tests, reactor modelling and basic reactor study areusually required for the scale-up of new and/or existing chemicalreactors, for new as well for existing chemical reactions.

Quite often a natural maximum appears to exist in the scaling-up processof chemical reactors. Further scale-up would introduce too manyuncertainties in the extrapolations based on the developed reactormodels and/or is simply not practical.

The present invention tries to find another way for the scale-up or thefurther scale-up chemical reactors. Rather than simply increasing thesize of an existing reactor (including adaptation of the reactorinternals, catalyst beds, mixing internals, cooling system, feedlines/feed distribution, product withdrawal etc.), either in diameterand/or height, two or more reactors of a certain, preferably identical,size are combined and operated as one single unit. The common feedlines, i.e. gas and/or liquid reactor system feed lines, are dividedinto as many equivalent streams as there are reactors and introducedinto the different equivalent reactors. Cooling and/or heating systemsare shared between the reactors. There will be one or more commonproduct discharge lines. The reactors are operated as one single unit.The control of the reactant feed to the reactor system is carried out bymeans of managing the feed flow (amount, temperature, composition,pressure etc.) in the one or more common reactant feed lines. There isin the single unit operation no individual control of each reactorsections. The control of the total product flow of the reactor system inthe single unit operated is done by managing the product flow in the oneor more common product discharge lines. In this type of operation thereis no individual control of the product discharge of each reactorsection. Thus, it is not possible to take one or more reactors out ofoperation. Only the complete reactor system can be taken out ofoperation. It is not possible to influence the condition in one of thereactors in a different way as in one of the other reactors. Turning ofone of the reactant feed lines will result in the fact that none of thereactors will receive the reactant feed stream any longer. Closing oneof the product discharge lines will result in the fact that none of thereactors will be able any more to discharge its products. Independentheating or cooling of the reactor sections is not possible. Reactorcontrol will be based on information obtained from all reactors present.A runaway in one of the reactors cannot be solved by closing down thereactor involved. It has to result in the shut down of the completesystem. Feed stream control is carried out by control of the common feedgas/liquid reactant feed lines.

The present invention therefore relates to a reactor system suitable forcarrying out chemical reactions, comprising one or more common reactantfeed lines, two or more single unit operated reactor sections and one ormore common product discharge lines.

A main advantages of the present reactor system is the fact thatscaling-up becomes easier. For instance, when a reactor of a certainsize has proven to perform its tasks well, there is no need for afurther scale-up of the reactor. Combining a multitude of similarreactors and operating it as one single unit with common reactant feedlines and common product discharge lines will result in the desiredscale-up. Or, in the case that a certain (large) scale-up for a specificreactor is required, the scale-up can be limited by using e.g. three orfour reactor sections operated as a single unit. The scale-up in thanreduced by a factor three or four. Further advantages are the lowerweight of the reactor, making transport/handling/lifting easier. It willbe appreciated that the size of a reactor may be restricted by workshoplimitations, road limitations, bridge limitations, lifting equipmentlimitations etc. The smaller size of the reactor may result in the factthat more companies are able to produce the reactor. Also simultaneousproduction by one or more vendors will be possible. As the reactorsystem is single-unit operated, there is no additional workforce neededto operate the unit from the control room. From a process control pointof view there is no difference between one large reactor and the reactorsystem of the present invention: the reactor system of the presentinvention is operated in the same way as one single large reactor. Ingeneral, the heat-up/cool-down rates for the reactor system according tothe present invention will be faster than for one large single reactor.Some additional maintenance may be required, while also a somewhatlarger plot space may be required. However, these small disadvantagesare clearly set off by the advantages. In addition, maintenance withinthe reactor may be done quicker, as work will be divided over severalplaces.

The above described reactor system is especially useful for stronglyexothermic reactions. An example is the conversion of synthesis gas, amixture of carbon monoxide and hydrogen, into methanol or hydrocarbons.As these conversions are highly exothermic, it will be appreciated thatextensive cooling is necessary. This results in an relatively highamount of cooling internals inside the reactor, resulting in a reactorwhich reaches relatively quickly its natural limits in scaling-up.Another example is the oxidation of (lower) olefins, e.g. thecatalytical conversion of ethylene into ethylene-oxide in a multitubularfixed bed reactor. The reactor system is also suitable for biochemicalreactions.

The reactor system according to the present invention suitably comprisesbetween two and twenty single units operated reactor section, preferablybetween three and eight single unit operated reactor sections, morepreferably comprises four sections. Usually a reactor section willcomprise a more or less conventional reactor, i.e. an elongatedcylindrical reactor, which, when in use, will be a vertical reactor.Suitable reactor sections are the well known chemical reactors as tankreactors, (multi) tubular reactors, tower reactors, fluidised bedreactors and slurry phase reactors. See for instance Perry's ChemicalEngineers' Handbook (MgGraw-Hill Book Company, 6th edition, 4-24-4-27)and Chemical Reactor Design and Operation (Westerterp, Van Swaaij anBeenackers, John Wiley & Sons, 1984). It is also possible that thereactor sections are located in one large reactor. This will overcome anumber of the problems related to scaling-up, however, some advantagesas described above may disappear. Preferably, all reactor sections havethe same size. However, this is not essential, and different sizes ofreactors may be used. It will be appreciated that in that case measureshave to be taken that the feed is distributed in the desired ratio overthe reactors. Also cooling/heating systems may need adaptation. Thesingle unit operated reactor sections will be operated in parallel. Thereactor system does not comprise reactor sections which are operated inseries. Preferably each reactor section is a separated, individualchemical reactor, suitably comprising a shell (or vessel) and one ormore reaction zone.

In most cases each reactor section will comprises one or more catalystbeds. Also slurry reactors may be used. In view of the large heatgeneration in hydrocarbon synthesis from syngas, slurry reactors mayhave advantages over fixed bed reactors in terms of heat transfer. Onthe other hand major technical issues associated with slurry reactorsinclude hydrodynamics and solids management. In a preferred embodimentthe reactor sections comprise a multitubular fixed bed catalystarrangement. The tubes are filled with catalyst particles, the tubes aresurrounded by cooling medium, especially a mixture of water and steam.Thus, the reactor sections each comprise an indirect heat exchangesystem, which heat exchange systems are jointly operated. Preferably thewell known thermosiphon system is to be used.

Depending on the chemical reaction to be carried out, gaseous and/orliquid feeds are to be introduced in the reactor. All possible reactorflow regimes may be used, i.e. up-flow and/or downflow, cocurrent and/orcountercurrent. Also gas and/or liquid recycles may be used. In the caseof the synthesis of hydrocarbons, one common gas reactant feed line willintroduce the syngas into the reactor system. This feed is split up inas many streams as are necessary for the number of attached reactorsections, and fed to the different reactor sections. In the case thatgas and liquid have to be introduced in the reactor sections, there ispreferably a separated gas feed line and a separated liquid feed line.It is recommended that reactors of the same type are used in the systemaccording to the invention, preferably of the same size. In the case ofheterogeneous catalytic reactions preferably the same catalyst is usedin all reactor sections, although this is not essential.

Depending on the chemical reaction to be carried out, gas and/or liquidhave to be discharged from the reactor. In some cases slurry, e.g. amixture of catalyst and liquid, has to be discharged from the reactor.When gas and liquid have to be discharged from the reactor, this may bedone by means of a single discharge line, but preferably the reactorsystem comprises one common gas product discharge line and one commonliquid reactant discharge line. The above described reactor system maycomprise a gas and/or liquid recycle line between the common productdischarge line and the common reactant feed line.

Suitably the reactor sections in the reactor system of the presentinvention are identical. Size, catalyst, design, cooling capacity etc.are similar. This is the preferred option as reactor manufacture in thatcase is a simple duplication process. However, identical reactorsections are not essential. Different sizes may be used, as well asdifferent types of catalyst may be used. It will be appreciated thatmeasures have to be taken that a correct feed distribution over thereactors has to be made, depending on the differences in design,catalyst etc. Also the cooling capacity may be different from onereactor to another, resulting in different conditions in the reactorsections of one reactor system. It should be taken into account, thatonce different conditions are created in one or more reactor section ofthe system according to the invention, there are no possibilities tochange the conditions in one or more of the reactors, as the system isoperated as one single unit.

The hydrocarbon synthesis as mentioned above may be any suitablehydrocarbon synthesis step known to the man skilled in the art, but ispreferably a Fischer Tropsch reaction. The synthesis gas to be used forthe hydrocarbon synthesis reaction, especially the Fischer Tropschreaction, is made from a hydrocarbonaceous feed, especially by partialoxidation, catalytic partial oxidation and/or steam/methane reforming.In a suitable embodiment an autothermal reformer is used or a process inwhich the hydrocarbonaceous feed is introduced into a reforming zone,followed by partial oxidation of the product thus obtained, whichpartial oxidation product is used for heating the reforming zone. Thehydrocarbonaceous feed is suitably methane, natural gas, associated gasor a mixture of C₁₋₄ hydrocarbons, especially natural gas.

To adjust the H₂/CO ratio in the syngas, carbon dioxide and/or steam maybe introduced into the partial oxidation process and/or reformingprocess. The H₂/CO ratio of the syngas is suitably between 1.3 and 2.3,preferably between 1.6 and 2.1. If desired, (small) additional amountsof hydrogen may be made by steam methane reforming, preferably incombination with the water shift reaction. The additional hydrogen mayalso be used in other processes, e.g. hydrocracking.

The synthesis gas obtained in the way as described above, usually havinga temperature between 900 and 1400° C., is cooled to a temperaturebetween 100 and 500° C., suitably between 150 and 450° C., preferablybetween 300 and 400° C., preferably under the simultaneous generation ofpower, e.g. in the form of steam. Further cooling to temperaturesbetween 40 and 130° C., preferably between 50 and 100° C., is done in aconventional heat exchanger, especially a tubular heat exchanger.

The purified gaseous mixture, comprising predominantly hydrogen andcarbon monoxide, is contacted with a suitable catalyst in the catalyticconversion stage, in which the normally liquid hydrocarbons are formed.

The catalysts used for the catalytic conversion of the mixturecomprising hydrogen and carbon monoxide into hydrocarbons are known inthe art and are usually referred to as Fischer-Tropsch catalysts.Catalysts for use in this process frequently comprise, as thecatalytically active component, a metal from Group VIII of the PeriodicTable of Elements. Particular catalytically active metals includeruthenium, iron, cobalt and nickel. Cobalt is a preferred catalyticallyactive metal.

The catalytically active metal is preferably supported on a porouscarrier. The porous carrier may be selected from any of the suitablerefractory metal oxides or silicates or combinations thereof known inthe art. Particular examples of preferred porous carriers includesilica, alumina, titania, zirconia, ceria, gallia and mixtures thereof,especially silica, alumina and titania.

The amount of catalytically active metal on the carrier is preferably inthe range of from 3 to 300 pbw per 100 pbw of carrier material, morepreferably from 10 to 80 pbw, especially from 20 to 60 pbw.

If desired, the catalyst may also comprise one or more metals or metaloxides as promoters. Suitable metal oxide promoters may be selected fromGroups IIA, IIIB, IVB, VB and VIB of the Periodic Table of Elements, orthe actinides and lanthanides. In particular, oxides of magnesium,calcium, strontium, barium, scandium, yttrium, lanthanum, cerium,titanium, zirconium, hafnium, thorium, uranium, vanadium, chromium andmanganese are very suitable promoters. Particularly preferred metaloxide promoters for the catalyst used to prepare the waxes for use inthe present invention are manganese and zirconium oxide. Suitable metalpromoters may be selected from Groups VIIB or VIII of the PeriodicTable. Rhenium and Group VIII noble metals are particularly suitable,with platinum and palladium being especially preferred. The amount ofpromoter present in the catalyst is suitably in the range of from 0.01to 100 pbw, preferably 0.1 to 40, more preferably 1 to 20 pbw, per 100pbw of carrier. The most preferred promoters are selected from vanadium,manganese, rhenium, zirconium and platinum.

The catalytically active metal and the promoter, if present, may bedeposited on the carrier material by any suitable treatment, such asimpregnation, kneading and extrusion. After deposition of the metal and,if appropriate, the promoter on the carrier material, the loaded carrieris typically subjected to calcination. The effect of the calcinationtreatment is to remove crystal water, to decompose volatiledecomposition products and to convert organic and inorganic compounds totheir respective oxides. After calcination, the resulting catalyst maybe activated by contacting the catalyst with hydrogen or ahydrogen-containing gas, typically at temperatures of about 200 to 350°C. Other processes for the preparation of Fischer Tropsch catalystscomprise kneading/mulling, often followed by extrusion,drying/calcination and activation.

The catalytic conversion process may be performed under conventionalsynthesis conditions known in the art. Typically, the catalyticconversion may be effected at a temperature in the range of from 150 to300° C., preferably from 180 to 260° C. Typical total pressures for thecatalytic conversion process are in the range of from 1 to 200 barabsolute, more preferably from 10 to 70 bar absolute. In the catalyticconversion process especially more than 75 wt % of C₅ ⁺, preferably morethan 85 wt % C₅ ⁺ hydrocarbons are formed. Depending on the catalyst andthe conversion conditions, the amount of heavy wax (C₂₀ ⁺) may be up to60 wt %, sometimes up to 70 wt %, and sometimes even up till 85 wt %.Preferably a cobalt catalyst is used, a low H₂/CO ratio is used and alow temperature is used (190-230° C.). To avoid any coke formation, itis preferred to use an H₂/CO ratio of at least 0.3. It is especiallypreferred to carry out the Fischer Tropsch reaction under suchconditions that the SF-alpha value, for the obtained products having atleast 20 carbon atoms, is at least 0.925, preferably at least 0.935,more preferably at least 0.945, even more preferably at least 0.955.

Preferably, a Fischer-Tropsch catalyst is used, which yields substantialquantities of paraffins, more preferably substantially unbranchedparaffins. A most suitable catalyst for this purpose is acobalt-containing Fischer-Tropsch catalyst. Such catalysts are describedin the literature, see e.g. AU 698392 and WO 99/34917.

The Fischer Tropsch process may be a slurry FT process or a fixed bed FTprocess, especially a multitubular fixed bed.

The present invention also relates to a process for the preparation ofhydrocarbons by reaction of carbon monoxide and hydrogen in the presenceof a catalyst at elevated temperature and pressure, in which a reactorsystem is used as described above. Further, the invention relates to theproducts made in the Fischer Tropsch process. The present invention alsorelates to the preparation of methanol and to methanol as prepared, aswell as to a process for the catalytic conversion of ethane intoethylene oxide.

1. A reactor system suitable for carrying out chemical reactionscomprising one or more common reactant feed lines fed into two or moresingle unit operated reactor sections having one or more common productdischarge lines, wherein each reactor section comprises an individualreactor.
 2. The reactor system of claim 1, comprising between 3 and 8single unit operated reactor sections.
 3. The reactor system of claim 1,in which each reactor section comprises one or more catalyst beds. 4.The reactor system of claim 1, in which each of the reactor sectionscomprises an indirect heat exchange system, which heat exchange systemsare jointly operated.
 5. The reactor system of claim 1 comprising onecommon gas reactant feed line.
 6. The reactor system of claim 1comprising one common gas product discharge line.
 7. The reactor systemof claim 1 comprising one common liquid reactant discharge line or whichsystem comprises one common liquid product discharge line.
 8. (canceled)9. A process for the preparation of hydrocarbons by reaction of carbonmonoxide and hydrogen in the presence of a catalyst at elevatedtemperature and pressure, wherein the process is performed in a reactorsystem comprising one or more common reactant feed lines fed into two ormore single unit operated reactor sections having one or more commonproduct discharge lines, wherein each reactor section comprises anindividual reactor.
 10. The reactor system of claim 1 comprising foursingle unit operated reactor sections.
 11. The reactor system of claim1, wherein each reactor section comprises a multitubular fixed bedcatalyst arrangement.
 12. The reactor system of claim 4, wherein theheat exchange system comprises a thermosiphon system.
 13. The reactorsystem of claim 1 comprising one common liquid product discharge line.14. The process of claim 9, wherein the catalyst comprises a cobaltcatalyst.